Should spring steel has excellent comprehensive performance, such as mechanical properties (especially the elastic limit, ultimate strength, showed), play reduce resistance (namely elasticity decreased resistance, also known as relaxation resistance), fatigue performance, hardenability, physical and chemical properties, heat resistant, good low temperature resistance, oxidation resistance, corrosion resistance, etc.). In order to meet the performance requirements, spring steel has good metallurgical quality (high purity and uniformity), good surface quality, strictly control the surface defect and decarburization), accurate shape and size.
According to the steel classification standard, according to the basic performance, spring steel belongs to the mechanical structure with steel; According to the quality grade, belong to the quality of special steel, namely in the process of production need special strictly control the quality and performance of steel. According to our habits, spring steel belongs to special steel.
Spring steel according to the processing and molding methods, divided into two categories, thermoforming and cold forming, due to the different processing ways in the subsequent heat treatment way is different, specific as follows:
A, thermoforming spring heat treatment
10-15 mm diameter or thickness is greater than the big spring, multi-purpose hot rolled wire rod drawing steel wire or steel plate.
Processing and heat treatment as follows: the first spring wire heated to higher than normal quenching temperature under the condition of 50-80 ℃ hot roll forming, and then quenching + tempering temperature, excellent elastic limit and fatigue strength of tempered sorbite. Spring steel quenching heating should choose little or no oxygen oxidation equipment such as salt bath furnace, protective atmosphere furnace, etc., to prevent oxidation decarburization.
Spring steel after heat treatment and shot peening treatment, strengthening surface, produce residual compressive stress, improve the fatigue strength.
The technological process for hot spring steel, flat steel shear heating temperature after bending forming residual heat quenching + tempering + peening packaging.
B, cold forming spring heat treatment
Spring is less than 8 mm in diameter, commonly used cold drawn steel cold roll forming. Cold drawn steel wire manufacturing process and subsequent heat treatment, mainly the following three categories:
1) lead bath treatment of cold drawn steel wire
To wire drawing three times in a row, the total deformation of 50%, and then heated to above ac3 make the austenitizing temperature, then in the 450-550 ℃ isothermal treatment in lead bath, austenite into sorbite organization. After the yield strength of 1600 mpa, cold roll forming, in 200-300 ℃ annealing eliminating stress. The dongguan spring
2) wire annealing state
Steel wire drawing to the specified size, and then to annealing treatment. Steel wire after softening after cold roll forming, need after temperature quenching + tempering to obtain the required mechanical properties.
3) oil quenching tempering steel wire
Steel wire drawing to processing size, after oil quenching tempering. Strength of this kind of wire lead bath treatment is better than steel wire, but the performance is uniform, the cost is low. After the cold roll forming, to deal with the stress.